Numerous types of seals are known in the art. Seals can be made in the form of rings and can provide a static frontal sealing action. Seals can be used, for example, for connecting pipes. Seals can be produced by winding two spiral strips superimposed on each other and with different physical and mechanical properties. Typically, the first strip has a high mechanical strength, for example a strip made of steel, and provides support for a second strip made of a material with optimal insulating and sealing properties. Machines exist which form seals by means of a semi-manual operation, which requires constant monitoring by an operator, or automatically. EP 0,707,906 describes an automatic machine for the production of seals. Strips with different physical and mechanical properties are spirally wound onto a support ring. The described machine comprises means for feeding said support rings to a mandrel; means for feeding the strips to be wound to the support ring; an assembly for applying radial pressure onto said rings; and an assembly for welding one of said strips for starting winding and for closing the seal once winding has been completed.
These machines have a number of drawbacks because they do not have means for retaining the seal in the direction perpendicular to its axis of rotation, resulting in a lack of planarity of the finished seal. This causes defects in the final welds. The defects are worsened by the fact that welding is performed by an assembly in a circumferential position of the spiral distant from the position of the pressing assembly in the radial direction of the spiral itself.
GB 2,258,018 also describes a machine for producing seals in which a welding assembly is separate from the pressing assembly and the welding assembly is operated to move towards the seal in a direction perpendicular to the operating direction of the pressing assembly. The double device involves an increase in the dimensions, power supply means and control means for the synchronized operation of the two assemblies. Additionally, defects arise since welding is performed in a zone different from the pressing zone.
JP 8-226544 describes a conventional welding assembly, which acts on the metal strip at the start and at the end of winding; however, does not describe the position and interaction of the pressing assembly.
In each of the above-mentioned cases, performing welding in a position different from that of the pressing assembly, the steel strip tends to react elastically, since it is free along the section between the pressing point and the welding point, causing a loss of compactness of the seal in the radial direction.